Tissue ablation is used in numerous medical procedures to treat a patient. Ablation can be performed to remove undesired tissue such as cancer cells. Ablation procedures may also involve the modification of the tissue without removal, such as to stop electrical propagation through the tissue in patients with an arrhythmia condition. Often the ablation is performed by passing energy, such as electrical energy, through one or more electrodes and causing the tissue in contact with the electrodes to heat up to an ablative temperature. Ablation procedures can be performed on patients with atrial fibrillation (AF) by ablating tissue in the heart.
Mammalian organ function typically occurs through the transmission of electrical impulses from one tissue area to another. A disturbance of such electrical transmission may lead to organ malfunction. One particular area where electrical impulse transmission is critical for proper organ function is in the heart. Normal sinus rhythm of the heart begins with the sinus node generating an electrical impulse that is propagated uniformly across the right and left atria to the atrioventricular node. Atrial contraction leads to the pumping of blood into the ventricles in a manner synchronous with the pulse.
Atrial fibrillation refers to a type of cardiac arrhythmia where there is disorganized electrical conduction in the atria causing rapid uncoordinated atrial contractions that result in ineffective pumping of blood into the ventricle as well as a lack of synchrony. During AF, the atrioventricular node receives electrical impulses from numerous locations throughout the atria instead of only from the sinus node. These aberrant signals overwhelm the atrioventricular node, producing an irregular and rapid heartbeat. As a result, blood may pool in the atria, increasing the likelihood of blood clot formation. The major risk factors for AF include age, coronary artery disease, rheumatic heart disease, hypertension, diabetes, and thyrotoxicosis. AF affects 7% of the population over age 65.
Atrial fibrillation treatment options are limited. Lifestyle changes only assist individuals with lifestyle related AF. Medication therapy manages AF symptoms, often presents side effects more dangerous than AF, and fails to cure AF. Electrical cardioversion attempts to restore a normal sinus rhythm, but has a high AF recurrence rate. In addition, if there is a blood clot in the atria, cardioversion may cause the clot to leave the heart and travel to the brain (causing a stroke) or to some other part of the body. What are needed are new methods for treating AF and other medical conditions involving disorganized electrical conduction.
Various ablation techniques have been proposed to treat AF, including the Cox-Maze ablation procedure, linear ablation of various regions of the atrium, and circumferential ablation of pulmonary vein ostia. The Cox-Maze ablation procedure and linear ablation procedures are tedious and time-consuming, taking several hours to accomplish. Current pulmonary vein ostial ablation is proving to be difficult to do, and has lead to rapid stenosis and potential occlusion of the pulmonary veins. All ablation procedures involve the risk of inadvertently damaging untargeted tissue, such as the esophagus while ablating tissue in the left atrium of the heart. There is therefore a need for improved atrial ablation products and techniques that create efficacious lesions in a safe manner.